Bloodstruck
by GrowingAHead
Summary: An AU where Kaigaku turns into a demon a little early. Turns out, he has a rare constitution. He can only consume the blood of the first person he feasted on. That person happens to be his hated colleague. And the Demon Slayer Corps ends up taking TWO teams of demon-hunter pair under their wings. Kaigaku/Zenitsu pairing. Female Zenitsu. Manga spoilers up to current chapters.
1. Chapter 1

**So, when I first laid my eyes on Kaigaku, I had no opinion of him other than: 'that nasty bit o' jerka**'**

**About two weeks later, here I am, writing a fic about him. Is this some sort of Blood Demon Art-induced hypnosis?**

**Notes: Zenitsu sometimes refers to Kaigaku as 'aniki' – which can both mean elder brother or a senior. I heard that women do not use that word often but since Zenitsu is using that word in place of 'senior', I've just kept its usage.**

**Female version of Zenitsu retains the same name. She might sometimes be called 'Zenko', but only from time to time.**

**Zenitsu here is aged up by a year or so. (Fortunately, Zenitsu is canonically 16, older than his friends - so not 'too' much of a difference.)**

**Warning: Lots and LOTS of manga spoilers up to latest chapters.**

* * *

There's no shame in trying to survive.

Ever since he could think for himself, it had been Kaigaku's steadfast principle.

If that means becoming something other than human, becoming the very being that he'd been trained to annihilate, then so be it.

_It takes a while for a Breath User to become a demon._

After imparting that information, the Upper Moon No. 1 had left the now-former hunter to his own devices, unwilling to waste time waiting until he became a full-fledged demon. Kaigaku had been grateful for that. He wasn't sure he could stand the powerful demon's presence for more than he'd already endured.

It'd already been three days.

The first day had been spent in agonizing pain. As Muzan's blood bestowed upon him raged inside, seemingly rearranging all his cells.

When the pain was gone, he could feel _something_ had changed. He's grown averse to sunlight, which was a concrete proof of transformation. There was a frustrating restlessness in his body as if each of his muscles had become separate creatures. But no burst of power as he expected. No thirst or hunger even when he'd gone two days without consuming anything. Although he felt slightly dazed, like his brain was wrapped in a cotton wool. Was this normal? What if something had gone wrong...

Perhaps he only became a demon _properly_ when he had his first taste of human blood.

But really.

"Kaigaku?"

To think he'd run into this idiot first. She hadn't changed at all since he'd left. Still puny. Fidgety. Like a harassed chicken.

"Wha – Weren't you out on a mission? Uh, did you come back for a break?"

Of course, he'd been wandering aimlessly and his feet had taken him upon the familiar path. And with his perception so dulled...

"Or – is your mission – _here?_ Does – does that mean there are demons _in this area?!_"

Ha, you're not wrong about that.

The blond girl glanced around warily as she walked over to him. Unfortunately, in trying to spot any demonic presence, she failed to spot a protruding tree root and fell over. Her haori fluttered open to show a torn slit at the lower garment.

Revealing a bloodied leg.

His heart gave such a thump at the sight that it was like being punched from the inside.

"You're bleeding."

Kaigaku murmured as if in a dream. The junior disciple looked down at her own leg, blushed, and tried ineffectively to cover it with her haori.

"Oh. Um, I did scrape my leg against something while I was -"

Kaigaku wasn't listening. He stared at the bright red streak along the dirt-specked skin.

And the world changed.

Everything came into an abrupt focus. As if a sudden tide had cleared away the previous haze. In the dark of the night, the moon was almost blinding to his newly-sharpened vision. He could hear the harsh breathing of his lowly colleague. (Ah, 'former' colleague.) Smell the metallic tang of her blood -

Then the hunger hit.

It was a claw that grasped the whole of his being.

He gasped and stumbled.

"Kaigaku? What - why do you _sound_ like that -"

Through reddened vision, he saw the blond girl stand up.

That ridiculous tumble of yellow locks shown like a beacon under the moonlight.

_Do anything to survive._

_If it comes at the loss of others, so be it._

He didn't even feel himself move.

The next thing he was aware of was that they were both on the ground. With him upon her, the latter too stunned to even react -

His fangs tore into the bloodied thigh as easily as into a ripened peach.

Heat flooded his mouth. Assaulting his sharpened senses. Flowing throughout his body, turning the prickling restlessness into sheer power. He had never experienced anything this intense. He might have blacked out for a second for pure ecstasy.

A scream brought him back.

Scrawny arms pushed him away with surprising strength. He didn't resist. Too drunk on the blood to care. The force of the push tore a sizable chunk of flesh off the leg he was latching on. He greedily chewed the delectable morsel. He could imagine how he must look like, from the almost comical look of horror on the girl's face. His wet mouth broke into a grin. Lengthened teeth bit into his lower lip. He felt the trickle of his own blood as his nails - now more akin to claws - slashed his palm open. Exhilaration coursed through as those wounds immediately closed up and healed.

He had never felt this powerful. Invincible. Immortal.

So this was what it meant to be a demon.

He couldn't believe how he'd survived until now as a human.

"You're useful for once, Zenitsu."

Teeth chattering from shock, the girl fumbled for the sword at her side.

Seeing that, it suddenly occurred to him that the Final Selection for her was two months away.

He laughed at the stray thought. Honestly, he was surprised he bothered to remember.

She somehow did get the blade out. But by then, Kaigaku was upon her again, hauling her up easily with one hand. She yelped and grabbed onto his arm by reflex, the other hand doggedly clinging to the useless sword.

"Kaigaku! Don't – Let – GO! Gramps would - You – you can't -!"

"Don't you _dare_ tell me what I _can't_ do,"

Well, he'd be doing her a favor. It's not like she'd would survive the Final Selection. Better a quick, painless death by him. He'd offer her that much, as her senior.

… If she just kept still, just as she did whenever he bellowed at her. She blindly kicked and slashed at him, screaming all the while. In terms of damage, the latter was infinitely more effective. Kaigaku grimaced at the impact of each high-pitched crescendo seemingly piercing all the way into his skull. Wasn't she supposed to have keen hearing? It was a wonder she didn't kill herself with her own hollering.

He harshly pushed her head to the side and yanked down her haori. (Same pattern as their master's, he never could stand that either.) That earned him a blow to the side of his face with the butt of the sword – which actually managed to snap his head back. Kaigaku slowly turned to face the other – a familiar look on her, red and wet and puffy. But there was something that he had never seen before – in the set of the jaw and the eyes. Defiance. He was both impressed and irritated.

Zenitsu started another scream but it got cut off as the demon's mouth closed upon her neck. Kaigaku felt her freeze up. Which made the pulse beating frantically under the thin skin all the more pronounced. No wonder she whiplashed between being crazy and a state of near-stupor. With such erratic pulse. Just for a moment, he thought it a pity that this would still permanently once he sank his fangs in. He closed his eyes to savor that almost-pleasant throb against his lips while it lasted.

He narrowly dodged a blade coming from the side.

Clicking his tongue, Kaigaku stepped back, letting go of Zenitsu in the process. He spotted a man in the same uniform as his pull the girl back by the scruff of her neck.

"Are you okay? You're a student, right? Get back!"

"We heard about a demon sighting here. Thought it was just a rumor – "

"Is that – a Corps uniform?"

One of more practical members charged at him rather than asking pointless questions. Kaigaku evaded more out of habit. Unlike his fool of a colleague, these were official members in possession of Nichirin blades. But even they weren't a problem unless they cut his head off.

And right now, these low-ranking hunters seemed to move in slow motion for him.

He lazily knocked off the sword from another coming at him from behind. Then he grabbed and swung her in front of him. As expected, others hesitated facing the obvious human shield. Incompetents. No wonder the members other than the Pillars kept diminishing. To think he'd been one of them only a couple of days ago.

He sneered maliciously behind the thrashing woman. Then lowered his mouth towards her neck. Well, his former colleague can wait. She couldn't even move for fear behind the useless hunters. He could just whet his appetite before getting to her -

An abrupt bile rising up knocked the wind out of him.

_What?_ He shook his head to get his bearings_. Why_ –

He growled in agitation and tried again to bite into his captive's throat. Only to be hit by a stronger wave of nausea.

_The Hell?!_

He grit his teeth. Barely containing himself from vomiting right then and there. What was happening? It should've been the same as when he'd drank from Zenitsu -

On the third try, he'd almost clamped his mouth on the other's flesh. The repulsion was so great that he threw her away from him. He sank down on his knees, gagging.

He glared at the confused slayers dragging back their comrade. Even his vision had become blurry. But he could still make out –

One missing.

He lashed out behind a second too late. The crippling nausea got the better of him and the blade bit into his shoulder. Snarling more out of anger than any pain, he turned and twisted the arm that held the offending blade, forcing the hunter to drop his weapon. At the same time, his claws slashed at the hunter's neck, drawing blood.

Kaigaku didn't give himself time to hesitate and rushed at the other's throat. Even before his fangs dug in, the wounded flesh yielded blood to his mouth –

Kaigaku tore away retching. He dropped on all fours. This time, he did vomit, his whole body shaking from the force of it.

Making up in sense what he lacked in skill, the released hunter beat a hasty retreat. Calling out to his comrades:

"We won't be able to beat this one by ourselves!"

"But… that demon… doesn't look… doesn't act... normal…"

"… Do demons get sick?"

Kaigaku told himself that he'd _kill_ the last one for that, even if he couldn't eat him.

_He couldn't eat them._

He pulled himself up with effort, wiping his mouth. His uniform all bloodied from what he'd coughed up.

He glowered at the hunters. _Food. All of them._ He recited in his head experimentally, grinding his teeth for good measure. The resulting revulsion was immediate. Every single cell inside him rejecting the very notion. Almost causing him to lose consciousness.

"Oi, you keep back, you don't even have a…"

It was like a thinnest trickle of cold, pure water. Cutting through the nauseous haze and clearing the bile. Kaigaku gulped in the smell of that blood like a man on the verge of drowning trying to keep his head up. Heaving, he looked up to see Zenitsu push through the group of hunters, leaning on her apprentice's sword for support. Dragging her still-bleeding leg. Kaigaku felt his mouth open behind his fist, panting.

_Fuck._

_Fuckfuckfuckfuck. FUCK_.

Kaigaku turned on his heels. His own body fought him, longing to be near that enticing smell of blood, that presence. He squashed that urge by sheer will.

_Must get away. Away from her._

When he looked back for a brief moment, he caught a sight of the blond girl open her mouth – only to slap her hand over it. There she stood, shaking and muffling herself, until he turned away and was gone.

* * *

It was raining outside the cave.

Kaigaku curled himself up into a tighter ball.

Five nights. Six once the sun goes down.

He'd held onto the barest hope that his – 'condition' – would be temporary. Of course, deep in his heart, his very body – knew that it wouldn't be so.

For the past days, he'd tried to devour anything else – including wild animals, and even a demon. (A mayfly of one he'd come across by accident. The only damage it'd caused him was due to him trying to devour the horrified demon and getting the most terrible sickness yet. So great that the demon actually managed to run away.) All ending in failure.

He knew he was going to expire at this rate.

And his body wouldn't accept anything other than Zenitsu's blood.

He thought about kidnapping her. But how to keep her around? Dammit, he'd become a demon to be more powerful, and having to drag around a live human wouldn't help. He doubted the other demons – the Upper Moon especially – would be benevolent enough to turn a blind eye.

He wasn't even sure he could join their ranks anymore, as the Upper Moon had hinted previously. _He will call you when needed._

Kaigaku now understood what he'd meant. Ever since he'd taken in Muzan's blood, he'd been aware of an inexplicable presence inside him – something propelling him forward, watching behind his shoulder. Forbidding him from ever speaking of HIM.

Ironically, he could clearly feel what it had been from its absence. It was gone from the moment he'd drank from Zenitsu.

He'd even tested it by speaking that name out loud. _Kibutsuji Muzan._ Nothing. He was still a demon, but he was – cut free, so to speak.

Now, Zenitsu had taken residence in him instead.

That was the worst. He could _feel_ Zenitsu. Where she was. Whether she was sleeping or loitering about. Distance helped to diminish the presence, to the point where it settled into a weak buzz that just let him know she existed somewhere. But his whole being rebelled against being away so, pulling him back like a migratory bird following its inner compass.

He wanted to turn himself inside out and scrape out every bit of her blood that'd infected him, if that were possible.

Meanwhile, he had to avoid the Corps members. The previous group had brought in reinforcements but had failed to locate him. Right now, it looked like they'd figured he was long gone from the premises.

Which made him wonder, why hadn't Zenitsu inform them about him? For if she had, surely the search would be more persistent, and his master would have –

He pulled his legs in deeper into his gut.

He was no stranger to starvation. But he'd never suffered anything like this. His whole being pinpointed towards a single want. And the lack of fulfillment was driving him mad.

"Kaigaku?"

At first, he thought he was hearing things. Then the familiar voice pricked his ears again.

"Kaigaku! I know you're here! …. Somewhere,"

He must've been much weaker than he'd surmised, to not notice her approaching this close. He jerked his head up. The scenery outside confirmed his suspicion. He had not realized the sun had gone down, either.

"Would you just… Kaigaku - "

"Shut up, you moron."

Zenitsu whipped her head so fast that stray locks hit her own eyes. Kaigaku huffed in disdain as the girl let out a cry and staggered back.

He sat down on the ledge of the stone mountain where his temporary sanctuary was situated, looking down at the girl. It was half because he was too tired and half to refrain from flinging himself towards that delicious, seductive-smelling source of blood.

"What are you doing here?"

"What happened to you?"

There was a pause after the simultaneous questioning.

The girl was shaking from the cold. Trying to shield herself from merciless rain with her sleeves. Her miserable, pouting face proclaimed: _'THIS is how much my life hates me.'_

Well, that was _his_ line, at the moment.

Kaigaku was the first to break the silence.

"If you can't tell, you're more of an imbecile than I initially thought."

"I – I worked up a lot of nerve to look for you, you know!"

Kaigaku didn't even grace that with a reply. Now he knew that one thing bigger than her cowardice was her stupidity. Wandering this far out at night, knowingly looking for a demon.

As if she could do anything about whatever that had befallen him -.

He could see her breath mingle into a tiny mist-cloud in the night air. Could feel the warmth of her even from where he perched.

He dug his hands into the rock to keep his anxious body at bay.

"What are you doing here?"

The repeated question seemed to have gotten through the girl's thick skull.

"Let's - let's go back. We can talk to Gramps. I'm sure he can figure something out -"

He snorted derisively.

"What, like cutting my head off?"

"Can't you see I'm _trying_ to not let that happen?!"

The sheer cheek of her. To think that she could 'let' anything regarding him.

"So why are you?"

Zenitsu hesitated. When Kaigaku growled impatiently, she blurted out.

"You - you didn't kill them. The Corps members."

"I tried to kill you."

He could practically hear Zenitsu gulp.

"Well - you didn't."

Kaigaku gnashed his teeth in a very demon-like manner. Zenitsu flinched but didn't back away.

"And you - sounded... panicked and... confused. Scared."

Kaigaku gripped the rock ledge so hard that a part of it crushed to dust in his hand.

"So - if you can just, just -"

"Why do you care? I know you hate me just as much as I hate you."

Her already pale face nearly turned blue. Then she hung her head so those preposterous ginkgo locks hid her face.

"But you're - Gramps's successor... And, and, you're my aniki -"

"I'm not your ANYTHING."

Zenitsu cowered with a hand over her head, as if the sheer venom in his voice had physically hit her.

"Please, Kaigaku- think of Gramps. He'll - he'll take care of this. I -I'll help too -"

Without any memory of having crossed the distance between them, Kaigaku found himself with a hand around her throat. Her gasp was squeezed into a choking gurgle as he slowly lifted her.

"Help? HELP?! YOU?"

The sword at her side clanged against him when he shook her. He despised _that_ almost as much as the haori she wore. Despite the whining, despite the escape attempts, despite everything -

She was never without a sword at her side.

"You've been NOTHING but HINDRANCE."

He'd have hated her less if she'd given up. If she hadn't learned the First Form.

To have the _gall_ to learn it when she couldn't even use it in an actual battle.

"Do you know why I became a demon in the first place? Do you?!"

Heedless of hands desperately scratching at his arm, he tightened his hold.

"It's because of _you_. It's all _your_ fault. If you hadn't - _been _-"

_'Kaigaku, after the Final Selection, you and Zenitsu will both be my -'_

And now, to be tied to this pathetic slip of a girl forever? What had he done to deserve such fate? He tried. He trained so hard - trying to survive -

He'd rather -

"I should devour both you and the old man and be done with it - "

Brown eyes flared open. Flailing hands grasped the demon's wrist in a sure grip -

Lightning struck at that moment.

And Zenitsu was flung into the air.

For a second, Kaigaku just watched the yellow form float through the lighted sky like a leaf. Strangely detached. The whole scene seemed to play in slow motion, something not real.

He only came to his senses as Zenitsu was about to go over the edge of the ravine.

Her body would shatter, at this height.

Shit. SHIT.

Kaigaku lunged. Kicking off the ground to gain speed. He reached out for her but it looked like she was going to smash into the opposite cliff in her descent -

The girl spun, seeming to spring off from the air itself, landing on her feet perpendicular to the cliff side she'd been about to crash into.

With her hands on the sword.

"Thunder Breathing. First Form."

And Kaigaku was completely unguarded.

"Thunderclap and Flash."

Lightning split the sky once more.

As thunder rolled in belatedly, Kaigaku blinked at the spinning night sky.

_It can't be._

From the corner of hectic vision, he saw his body below crash down onto the rocky ground, spurting blood from the neck. Which ended in a stump.

If it'd been a Nichirin blade, he'd be dead.

_She cut me? She managed to - that worthless piece of –_

Impossible. That wasn't right.

He - was his severed head _him_? - dropped next to his body. The fall hurt more than the cut. How fast it must've been for him to not see, let alone feel -

The skewed sight of the girl crouched in the finishing stance greeted him.

Rain thudding upon her body fizzed to steam. She shuddered.

And snapped her head up with a cry.

She stood frozen for a moment. Took a step back. Realizing how dangerously close she was to the ledge, she jumped back screaming, crawling away on all fours.

Then she turned and came face to face with Kaigaku.

She looked back and forth from the head laying on its side to the bloody body next to it.

The howl that emitted from her mouth drowned out even the thunder.

"WAAAAAAAH! Kaigaku! What - You're - you're not - don't tell me -"

Trembling, she stretched out her twitching fingers. When the head scowled, she fell back on her haunches, bursting into tears.

_Are you KIDDING me._

"What - what, what happened?! Didn't you - throw me - "

"What's _wrong_ with you, dumbass?"

"Aaaah! You, you're talking! But your head, I mean, you're a, a, a _head_..."

Bewilderment took over anger and humiliation. Kaigaku sighed and grit out the next words.

"Just. Get. My. Head. Back. On."

"Um, oh! Ah..."

Zenitsu gingerly put her hands forward, shuddering all over as fingers brushed his hair. Another yowl erupted when she accidentally touched the cut stump. _'There's blood! It's all over my hand!' 'Of course there is! Whose fault is that?!'_

She lifted her senior's head, trying not to make eye contact. Just before moving towards the body, she faltered, and spoke. With her face still turned away.

"I'll, I'll, I'll - only do it if you promise to not hurt Gramps." Then she added almost as an afterthought. "And... maybe not eat... anyone...?"

Rage fleeted over the demon's features. Only to dissipate.

After a moment, the head began to wobble. Astonished, Zenitsu stared.

Kaigaku was laughing.

"I _can't_."

"What?"

"I can't eat anyone."

His voice quivered between a laugh and a sob.

"I can only consume your blood."

* * *

Kaigaku had always known he was special. And he was.

Just not in the way he'd expected, or hoped for.

* * *

**End Note: That was… a much longer setup chapter than I initially thought.**

**I think the happiest part about this AU is that Gramps lives.**


	2. Let's Talk about This

**cielo1827 : Thank you for reading! And here is the next chapter. Hope it keeps your interest!**

**Wanderstar : Thank you so much! Yes, definitely more chapters coming. I hope I can turn them out a bit faster. :)**

**Notes: In this chapter, Master Kuwajima may seem a little… stern in his training policy. But then again, considering the death rate in the Final Selection, no training is too strict for an apprentice Demon Slayer.**

* * *

Of course the stupid girl would drop unconscious on their way down.

And of course she'd be burning up with fever because she was just crazy enough to look for a demon during a nightly storm. _Of course._

He'd initially just hauled her up like a sack of rice over his shoulder. But she kept slipping off. And it belatedly occurred to him that it might not be in his best interests if she got the brunt of the rain and got sick even more.

Eventually, he ended up carrying her in his arms. _Then _he noticed the dark stain spreading over her lower garment. The bite-wound on her leg. The _idiot _hadn't even managed to treat it properly. Upon cursory inspection, the wound didn't look infected but the flesh around it was hot. Kaigaku wondered if this was the real reason she was like this. She likely hid it from the master too because he'd never let any injury get this bad. The girl was just a _mass _of problems. Kaigaku felt a pang of sympathy for his master.

He was startled to realize how close his face was to the bare, bleeding thigh. He didn't even any memory of tearing the lower garment.

He'd drank from muddy waters. Eaten garbage that others threw away. Fighting his corner against stray dogs. Even then, he told himself: there's no shame in trying to survive.

But he felt it now as he lapped blood off the unconscious girl's thigh. The first time had been no different than a meal or a hunt. But this felt like… something lower than stealing. The fact that her blood was even _more_ sweet and headier than last time made it worse. His whole body seemed to give a contented sigh, clamoring for more. It took all his willpower to not bite deeply into the rain-chilled flesh.

In retrospect, there were some things he should've considered. One: his demonic strength had carried him further down the mountain than he'd assumed. Two: their master would already be out and about looking for his student, whose escape attempts were habitual offenses. Three: it was a given that he'd be intoxicated by a few drops of Zenitsu's blood after so many days without nutrition, thereby depriving him of any sense to notice another presence approaching.

So of course Kuwajima Jigoro came upon the sight of his pupil with his face buried between his other pupil's legs. Of course he did.

* * *

It could be assumed that a lot of thoughts went through the older master's head in that short moment. Some of which probably consisted of: 'They're young bloods, after all,' and: 'A snake bite. It must be a snake bite.'

All the while, his old hunter's instinct was kicking at the back of his mind, trying to get his attention. Although the old man was dismissing it out of hand because what it told him was impossible.

Then Kaigaku lifted his head.

There was another moment where all previous thoughts in Kuwajima's head was replaced with one, terrible fact.

Demon.

His pupil was a demon.

And Kaigaku could see all that, reflected in his – if he could still claim that - master's eyes.

He doubted that he could've avoided the blow if he hadn't been a demon. Raindrops got sliced in the space that he'd occupied a millisecond ago. Kaigaku had not expected the old master to _move_ like that. With a wooden leg, no less. Although, he needn't have moved. The retired Pillar's cane was probably a hundred times deadlier than a regular Mizunoto's sword but it was no Nichirin steel.

"Master, listen –"

"What have you done to Zenitsu!"

"Nothing!"

_Bit off a chunk of her leg. Flung her over the ravine. But she cut my head off. That should wipe the slate somewhat clean._

"You have her blood on your – !"

_Oh, fuck. _Without thinking, Kaigaku licked the smear off his lips. Probably not a good move considering the circumstances. He dodged another blow. Damn reflex. Beat into him during his training days. Kaigaku seriously considered hurling the girl at the old man just to buy some time.

"Why did you let yourself become a demon!"

_Hell with this._

Another strike over the head. This time, Kaigaku raised one arm.

The cane broke.

A chip of wood whipped past the girl's – still held in the demon's arm – brow, drawing a thin trickle of red. That made the old man stop. Never had Kaigaku seen a more dreaded, nor so anguished, an expression on his master. Which compelled him to speak _something_ in his defense.

"I didn't harm her."

_Well, not _now.

"Do you expect me to believe – "

All the pent-up frustration chose that moment to burst out of Kaigaku. The growl that preceded his words definitely didn't sound human.

"Take your _miserable successor_ and see for yourself! Let her tell you since you obviously don't believe me!"

_Like you never believed in me for anything._

The old man actually leaned back a little. The hand holding the broken cane wavering. Which goaded Kaigaku even more.

"If you can spare me a few moments until this useless luggage –" He thrust the girl forward so that she teetered dangerously – "manages to rouse herself, which, was _her_ fault to begin with –"

"_Be quiet."_

Both the young demon and the old master looked down at the source of the sudd_e_n voice.

Zenitsu's eyes were only marginally open. Kaigaku was sure she wasn't seeing anything because even those thin slits were filled with tears about to overflow.

Sluggishly, as if she were moving underwater, she lifted an arm and grabbed the hem of his clothes.

Then she raised her other arm to connect a weak, trembling fist to his chest.

"You… you say _hurtful_ things even in a _happy_ dream,"

The pounding increased, her body quivering with the effort. But it was like a child's tantrum. Kaigaku wouldn't even have noticed if he weren't watching those cotton-ball blows land on himself.

"Can you _not_… be that way just until I wake up…? Then I'll tell…"

The last blow listlessly slid down the demon's chest.

"…tell... Gramps… so… can you…"

Zenitsu's head dropped to the side, resting on the very target she'd been pounding on. Her harsh breathing settling down.

Both men wordlessly looked at the sleeping girl for a full minute. Then they simultaneously looked at each other.

Kuwajima sighed and lowered his hand.

"All right, Kaigaku. Let's hear it."

* * *

_Hell with ALL this._

Kaigaku kicked the iron door. Which thrummed but didn't budge.

The shed he was locked up in served as a surprisingly sturdy makeshift prison. He wasn't even _aware_ that his master had something like this. But then, his master had been one of the Pillars who'd captured demons for the Final Selection. So perhaps this 'shed' had once been used for that. The fact that it was windowless with no light getting in strengthened the theory.

And he was now one of the caught demons. Until the leader of the Corps decided his fate.

After depositing the sleeping girl in her room, Kaigaku had told his story. Mostly truths. He was too tired to do otherwise. He faltered, however, when his master asked just how he'd become a demon in the first place.

At that moment, Zenitsu had burst into the room. Stumbling on all fours and flopping on her belly between them. Barely woken up and still feverish. Then she started babbling incoherently with sobs mixed in between. The gist of it ran thus: _'Gramps! Kaigaku is a demon! But don't cut his head off! It was – it was an accident! And he didn't kill or eat anyone! He can't! Just cannot! Anyway, I was just with him – and – then I was… in my room… what happened?_'

At that point Kaigaku smacked the back of her head so that she tumbled over the tatami floor.

"Wha – Kaigaku?"

"You idiot -. Will you stop your crazy yammering?!"

"Um – what –"

The girl slowly sat up, arranging herself into a sort of messy heap. She dazedly looked back and forth between her senior and her master. Quite unaware of her disheveled clothes falling open as she did so. Kaigaku grit his teeth. It wasn't so much that the exposed skin threatened the air of propriety. It was that it looked, smelled, irresistibly delicious.

"I know you don't have any sense but do you not even have any shame - cover yourself up, at least!"

"Wahhh! Don't do it _yourself_! Let go! You – you - _per _-"

At that point their master had risen and with his broken cane, whacked both of them across their heads.

* * *

Kuwajima Jigoro had to admit that his 'demon pupil' noticeably lacked the blood-lust that had hold of all young demons. Yet even Kaigaku didn't expect the old man to casually cut his own hand and shove it right up his pupil's mouth. Kaigaku had to swallow humiliation while he again regurgitated what meager amount of blood he'd had. At least he'd passed the test.

A letter was sent to the Ubuyashiki House via crow, detailing the unusual circumstance.

For all he knew, a group of seasoned hunters might be swarming the place in lieu of a reply the next day, ready to slit Kaigaku's throat. Well, next day in a manner of speaking, for Kaigaku had no idea how much time had passed since his imprisonment.

And so here he was, awaiting judgment.

Alone with his hunger.

His master hadn't asked him about it when he put him in here. And Kaigaku had been too proud to beg. Perhaps the old man thought it a fitting punishment for his demon-turned pupil.

What had he been thinking? Perhaps kidnapping the damn girl _had_ been a right idea. It might be difficult in his current state, but if he gave it all, perhaps he could break down the walls before the hunters came for his head and -

He rubbed his neck and only then realized the absence of the jade he always wore. Of course, when she cut his head off...

As if he needed another reason to despise her.

Well, speak of the devil.

He took a deep breath. Waited a beat, and spoke.

"What are you doing here, you piece of dirt?"

He heard her give a little squeal.

"How did you -"

_I could practically _feel_ you flinch_. Kaigaku only replied with a snort.

His neck felt strangely light and exposed without the jade. He couldn't remember a time when he'd been without it. He found himself keep picking at the skin there.

There was a light bump. Zenitsu had slumped down against the iron door. He could tell she was _exhausted_.

"... I feel like I'm gonna die,"

_I didn't ask, you laggard._

"Gramps put me on a harsher training routine ... which I didn't know was _possible._ And no meals for a week, to boot. As a punishment for not telling Gramps about you. Well, Gramps is going to do the no meal part himself..."

"You don't seriously expect me to _pity_ you for that, do you?"

Especially the _no meal_ part.

"Well, no..."

There was a noise that no doubt came from an empty stomach. Followed by a series of embarrassed coughs.

"Um, so how are you holding up?"

"How do you _think_? Never mind, you _don't_ think."

A silence that had a very Zenitsu-ish sagging quality. Then, a near whisper:

"I... er, think it's going to be okay, about the letter..."

Kaigaku didn't bother replying. No more words were forthcoming from the other side of the door either. Just as Kaigaku wondered if she was about to go away, the other's voice came back.

"Gramps doesn't _sound_ worried. So... that means he thinks it's going to turn out fine."

The only instance the word 'close' would be used in relevance to the two Thunder Breathing disciples would've been strictly with regards to describing the physical distance between them. But since they _had_ lived together, they couldn't help picking up on certain aspects of each other. So Kaigaku knew what Zenitsu meant by 'sound' right now.

"Or, the fate of the demon-turned pupil isn't all that much to worry about."

It occurred to him a second too late that his life wasn't the only one on the line. For he knew that Kuwajima Jigoro wouldn't hesitate to slice _his_ own stomach to take responsibility if Kaigaku was to be beheaded. But he shoved what little guilt that threatened to rise with boiling resentment. Perhaps the old man's loyalty to Ubuyashiki was too deeply rooted that he probably believed cutting out his own innards was of no consequence.

Zenitsu spoke again.

"No, I've only heard him really worried twice. Once when I got hit by lightning ..."

A great amount of fondness, tinted with a bit of smugness, carried over. Which only fanned Kaigaku's irritation.

"... and the other time was when you went to your Final Selection."

Kaigaku made as to retort, and just clenched his teeth. Something stirred in the deep recess of his mind. Something he wasn't used to. He quenched it. Forced sneer into the next words.

"No wonder he wanted a _backup successor_ if he thought me that weak."

He expected a sob – tinged defense of his master. But what came was a question, floating on an eerily calm tone.

"... Why did you become a demon, Kaigaku?"

What right did _she_ -

"I know it wasn't an accident."

Kaigaku let out a derisive huff.

"Funny, _you're_ the one who insisted that it _was_ one."

Which was true. After the chaos that was Zenitsu had been somewhat doused, their master had again pressed just _how_ this had come about. To Kaigaku's surprise, Zenitsu was the one who repeated that 'it had been an accident'. Insistently so. Giving half-glances at Kaigaku. So Kaigaku had given a 'modified' version of the story - of having crossed an Upper Moon. He didn't so much lie as to omit certain details. And if such led the listener to interpret the event as the demon having 'forced' Muzan's blood into the young hunter for some vicious enjoyment of his own, well, Kaigaku could hardly be faulted, could he?

But now, _she_ was...

"I said that, but I know... it wasn't true. Unlike when you were talking about... um, that you could only... drink, er, my blood. You sounded different. I can tell."

"That's rich coming from someone who got swindled by some lowlife and had a stranger pay off her debt."

_That_ shut her off.

Silence reigned for a while. Which wasn't to his advantage. Kaigaku rubbed his face and snarled as her smell - her blood's smell - wafted over to him.

"So why did _you_ lie to the master?"

His words came out muffled with his head buried in his arms. He didn't really expect a reply. It was just to break the ringing silence filled with her presence. But a feeble sound seeped through.

"... Gramps would be sa – he'd have… not have taken it well. And, well, you're my - an aniki. "

Kaigaku hated that he could perfectly picture her right now. Her whole body drooping like a mouse caught in a downpour.

"Was it really because of… me?"

He was honestly surprised she remembered, had even heard what he'd said, considering the circumstances.

"... Forget it."

He sighed out the words. The reply from the other side felt decidedly sulky.

"Well, all you had to was wait for two months. Then I'd been out of your hair for good."

_Yeah. I could've waited. While being digested inside an Upper Moon's stomach_.

"I'm sorry."

This was so out of the blue that Kaigaku actually turned to face the door.

"What?"

"I mean, the Final Selection. I - I - now we're both screwed."

Kaigaku rolled his eyes.

"None of this would've happened if you'd just left, like I told you so."

_If you hadn't clung so._

"Nothing's stopping you from running away from the Selection. It's not like the master's going to hold your hand and take you there. So why don't you?"

There was a shuddering sniff.

"... Because I'd rather fail Gramps than betray him."

It shouldn't have stung as much as it did. After all, the only one he had loyalties to was himself. So it didn't count as betrayal...

It still stung.

The girl was a _curse_.

"... I suppose you can't convince Gramps to change his mind about the Final..."

"_SHUT. UP_."

The steely chill in his voice did the job. She obeyed. For once. Even her presence changed. In a manner that reminded him of when they'd come across a wild –possibly rabid - dog once. Not long after their master had taken the young girl under his wing. Zenitsu didn't even scream or break into a panicked run as he'd expected. She'd just shut down. As if she'd morphed into something inanimate. Very much like that time, she just stayed still on the other side. Like a stone that'd happened to roll up against the door. Kaigaku could have enjoyed a malicious glee at that. But the problem with her becoming a rock was that she was unlikely to roll away by herself.

The thing was, these quiet intervals were becoming more and more unbearable. With nothing to distract him, her proximity was a torture. His muscles ached as if his flesh itself stretched towards her. He desperately tried to focus on something else.

_All he had to was wait it out, until her Final Selection -_

Granted, he'd shared Zenitsu's opinion on that until -

He'd might as well sate that curiosity.

"All right, are you really pulling my leg or what?"

"Huh?"

"After what you've pulled, the Final Selection's a concern?"

The silence this time was filled with confusion and exasperation of equal measure. Until Kaigaku ground out: "You - cut me -"

"But you did it _yourself_ -"

"_What_."

"That's what must've happened. I sort of… drop off to sleep every once in a while. While training."

There was a sigh so deep that it could have left a hole in the ground.

"I... tried to hide it from you and Gramps. But I guess that's what happened last night. I must've unconsciously had my sword out while I fell and... you jumped... maybe you weren't used to your, er, demonic speed or something? So..."

Kaigaku banged the back of his head on the door. Hard enough that the resulting clang made Zenitsu gulp loudly.

"Do you... _dream_ during those... unconscious intervals?"

"Uh? Um, yes?"

"About what?"

"... I'd rather not say,"

"Why?"

"Because you'll only make fun of me."

Kaigaku wanted to let out a scream that'd outdo his colleague's best. Instead, he started to breathe, per his training routine. Funny how one falls back on the familiar.

He gave up on the topic.

"So this is why you came? To unload your woes onto me?"

A pause that could be described as _awkward_. Then: "You, um, must be, er, hungry - er, starving?"

Kaigaku angrily swiveled towards the door a second time -

\- And was startled to see the heavy door creak open. A yellow head peeked through.

"How did you -"

"I can pick locks," murmured the girl as she cautiously squeezed in- as if afraid to open the door any wider - and closed it even more carefully. "Well, _this_ lock, at least." She gestured back at the door. "Gramps used to lock me up here when I tried to run away once too often."

'Since I had a lot of time in here ...' She sheepishly scratched her cheek as Kaigaku stared. When he'd said that their master had bestowed undeserved attention on his hopeless colleague, he wasn't exactly thinking about something like this. At the same time, he had to wonder just how _bad_ was the girl's escaping habit that their master was forced to use a prison that'd hold a _demon_.

Zenitsu tentatively approached him. She looked pretty much like Kaigaku had envisioned her: Head lowered, face shadowed under the bright locks. Like when he'd thrown a peach at her while yelling.

"I... I mean, you've gone without anything for - nearly a week, right?"

_Except for a couple of sips. Which probably got expelled thanks to the stunt the master pulled_.

"So - if, if it's really only my -" She bit her lips, fidgeted with a stray lock of her hair near her neck.

_I don't need your pity nor charity. If you want to be helpful, then get the hell out of here_ – was what he'd been about to say, but his body wasn't interested in his thoughts. In fact, it chose to straight up trample on his dignity by taking hold of the figure in front and yank her down.

Zenitsu gave a high-pitched yelp as she was roughly pulled flush against the demon. She made as to struggle out of his grip by reflex but went rigid as soon as Kaigaku put his mouth against the side of her neck. Wet locks of hair stuck to his cheek and Kaigaku minutely wondered what the girl had been doing again out in the rain but then he inhaled a faint whiff of soap on her skin. He almost laughed at the fact that she bothered to wash before coming here. When he knew that she used to just pass the day into next with all the sweat and dirt from the training intact, too tired and uncaring. As if this time, she was consciously readying herself for-

A sharp little cry as the demon's fangs dug into the flesh. Which quietened to little sobs as he sucked at the blood that welled up. Kaigaku groaned at the pleasurable burn that flowed through his mouth, throat, down to every stretch of his veins. It wasn't _just_ the blood, but everything that accompanied the act - the smell and the heat and the feel of the flesh that yielded under his teeth. His body hummed to the beat of the other, everything that was - her _life_. He couldn't remember being so - _filled_. Satisfied.

Kaigaku licked down the line of the collarbone. Loathe to miss even a single drop. He absently took in a scattering of freckles that lightly dusted the juncture of her neck and shoulder. Funny how he'd never noticed it before. It made that particular place look strangely fragile.

"Mmph -"

The small sound made him detach himself a little to look at the girl. Zenitsu was biting down on her two fingers, hard enough to draw blood herself, trembling with the effort to keep those little whimpers in but Kaigaku could still hear and see her heavy breath congeal in the moist air. Her whole body felt tense and tight. Skin flushed all the way up to the tips of her ears. Eyelashes glistening with teardrops. He wondered if that was from pain. But she looked more - as if she were being -

"Stop looking like that,"

"Eh? Ah?"

Kaigaku held her away from him. He felt his own face heat up. Not solely from the blood that infused him.

"Like you're - as if this were -"

Kaigaku trailed off, not really sure _where_ his thoughts were taking him, only certain that he didn't like it. It seemed Zenitsu shared his sentiment.

"I, well, I can't help it! It's just - a, a natural reaction! It's because you're making all that weird noise - "

"_I did not_!"

" - And, and, you really don't need to do that with your - your -_ tongue_ -"

"_I am not_ -"

"And all that, _heavy breathing_ -"

"Leave me out of your - your - perverted _fantasie_s!"

Zenitsu wiped her eyes and glared at him. Then she pulled her clothes up to her neck and stood abruptly. Although the effect was dampened by her feet wobbling.

"You know what? Fine! I was wrong to come at all! Wrong to think -"

Kaigaku's body pulsed greedily at the hint of its feast departing so early.

"Wait -"

Except he launched himself a bit too strongly. And Zenitsu's already precarious legs completely gave.

"Kaigaku, about you needing Zenitsu's -"

And of course, Kuwajima Jigoro came just in time to witness his two pupils all tangled up on the floor. Of course he did.

* * *

Kuwajima had dragged Zenitsu away by the ear. And Kaigaku's incarceration was now lengthened at least a week after they'd gotten a reply from Master Ubuyashiki. Until he could, per his master's words, 'control his animal urges.'

Kaigaku growled and sank down against the door again. Then he sighted a small bundle of cloth on the floor.

Frowning, he picked it up and unwrapped it.

Nestled inside was the jade he recognized. Tied with a different string.

Kaigaku looked down at it for a moment.

He slowly picked it up and let it dangle under his fingers, clicking his tongue as the jade spun unsteadily.

"... Can't even do a decent knot, that idiot."

Yet when he'd tied it around his neck, the familiar cold weight lent him some comfort.

* * *

**End Notes: Like many others, I am still surprised to find myself a fan of this boy who is a mass of issues. (That is putting it extremely kindly.)**


End file.
